A 19-year-old Georgetown University student told investigators that he learned how to manufacture ricin by researching on the internet on his iPhone, then bought the needed materials at Home Depot and a plant store, according to court documents.

Daniel Harry Milzman, 19, of Bethesda, Md., has been charged with possession of a biological toxin -- a federal offense -- after he told his residential advisor about the powdery substance earlier this week.

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The university said there was no immediate danger to students, but the ricin was strong enough to be lethal if inhaled or injected, according to the charging documents. Milzman told investigators he wore a mask while making the powder.

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Authorities were called to McCarthy Hall in the 3700 block of O Street NW early Tuesday morning after Milzman showed his RA the ricin. He had kept the powder in a plastic bag and sealed it with hockey tape, the charging documents said.

"There is no immediate threat to members of the Georgetown community," Chief Jay Gruber wrote. "The university consulted with the D.C. Department of Public Health, which informed us that anyone exposed to ricin would have presented with severe symptoms within 24 hours. This window has passed and there are no reports consistent with ricin exposure."